Piston



Jan. 9, 1940. J. FLAMMANG PISTON Filed Oct. 21, 1935 new 1.... 9; 1940 2,186,375

UNITED STATES luvrarrrv OFFICE- PISTON John l 'iamniang, University City, Mo., asslgnor to The Sterling Corporation, St. Louis, Mo., a corporation of Delaware Application October 21, 1935, Serial No. 45,852 1 claim. (01. cos-11) This invention" relates to pistons and more with the usual ribs 5 and 6 firmly connecting particularly to trunk pistons of aluminum or the wrist pin bosses with the head. The head magnesium and their alloys such as may be used is, as usual, made of slightly smaller diameter in internal combustion engines. than the skirt and the latter is relieved in the 5 In the development of pistons of the character regions of the bosses as by beingv formed with a 6 referred to, and particularly where such pistons slightly oval shape, the diameter A taken across are made of aluminumior magnesium alloys,diflithe thrust or bearing faces being slightly larger culty has been encountered because of the fact than the diameter 13 taken along the wrist pin that the thermal'expansion of aluminum is much axis.

greater than that of cast iron; accordingly, an 1 The skirt is connected with thehead in the 10 aluminum piston will expand faster than the cast region of the wrist pin bosses in the manner iron cylinder in which it works. described but is separated therefrom by a cir- In pistons as heretofore constructed, some arcumferential slot or slots 8 and '9 in the region rangeinents have been suggested to render the or regions between the bosses. The circumferen- 15 piston skirt resilient and yielding, so that extial slot or slots may be in the lower ring groove II pansion upon rise of temperature may be taken as shown in Figures 1 and 2 or therebelow as up or compensated for by the resiliency or yieldshown at 80 in Figure 6 in which case the diing of the skirt. Such resiliency or yield has ameter of the skirt portion above the bottom been sought by slotting or cutting the skirt cirof the circumferential slot of slots is reduced cumferentially and vertically so as to render cerin the same manner as is the head. 20 tain portions thereof free to move without re- The skirt may be provided with vertical slots straint by the adjacent portions. This, however, 1 running generally along the skirt but terminatnot only rendered the piston skirt comparatively ing above the lower end 4 so as to leave the latter weak so that it was eventually distorted, but the continuous. These slots may extend from a point yield of the unrestrained portions resulted in I substantially midway of the length of the skirt as the restrained portions of the skirt bearing upwardly as shown in Figure 1 and may join against the. cylinder, resulting in wear in spots the slots -8 at the top, the portion between the or zones. vertical slots thus forming an upwardly-extend- One ofthe objects of this invention, therefore, ing tongue. The slots 4 are preferably given an 80 is to provide a piston of the character referred inclination with respect to the axis of the piston to wherein theexpansion is not only'compenin order to avoid scoring of the cylinder wall; sated for but so controlled that the bearing of such inclination may, however, be moderate as the piston against the cylinder wall will not be shown in Figure 1 so as to connect with the ends in spots or zones. of the horizontal slot or the inclination may be 85 Further objects will appear from the following greater as shown in Figure 5 so as to connect 3 description taken in connection with the accomwith the circumferential slot at points between P y drawing in which: its ends. Thecircumferential and vertical slot- Figure 1 is a side view of a piston embodying ting may be only on one side as shown in Figure its invention. 1, but may be on both sides;' thus Figure 5 may 40 Figure 2 is a similar view showing the side betaken as corresponding to Figure 2.

pp i h Of Fi u 1.7 It has been found that when the tongue formed Figure 3 is a bottom view looking into the open by slots I and 8' is entirely free of the adjacent end of the piston. portions of the piston so as to be capable of un- Figure 4 is a longitudinal sectional view taken restrained movement it'glves away under pres- On line of Figure sure incident to the operation of the piston in 45 Figure 5 is a fragmentary view of a portion the cylinder, to such an extent that the actual the Same Side of the Piston as en in Figure 1, bearing of the skirt on the cylinder wall takes I-- showing another arrangement of the slot. 7, place at the points or zones 12 adjacent the Figure 6 is a fragmentary view of a portion tongue and in practice such bearing is readily of the piston showing still another arrangement indicated by worn spots or zones found on the 50 of the slotting. skirt after use. In order to overcome this difli- Referring now to the accompanying drawing culty, the upper end of the tongue is connected there is shown a trunk piston having a head I; to and supported on adjacent portions of the wrist pin bosses 2 and a skirt indicated generskirt by means of narrow bridges l0, and these ally at 3, the interior of the piston being provided bridges may be formed by lugs cast on. the inte- Q stant, while the expansion along the diameter B- 2 k 7 areas" rlor of the skirt, a hole being preferably preliminarily drilled in each lug prior to vertical slotting in order to receive the saw as it cuts the slot I. This is a procedure resorted to in slotting generally, as will be shown by preliminarily drilling holes at the ends of the vertical and horizontal slots. The bridges or lugs l2 merge into the skirts by fillets, as is usual in casting practice. The bridges may not only be formed by permitting the metal of the skirt to flow into the mold so as to form these bridges of the skirt metal, but

they may be formed of steel or other material placed in the mold and anchored in the casting by permitting the metal to flow therearound in a manner usual in'casting practice.

In the piston structure described, the action is believed to be as follows: The skirt is connected to the head in the regions of the wrist pinbosses but free therefrom in regions therebetween. The

expansion of the head upon rise of the temperature will be communicated to the skirt only at these points or zones of connection; accordingly the expansion of the head will impose uponthe portions of the skirt in the regions of the wrist pin bosses, the corresponding expansion. This expansion, therei0re,- takes place in the regions of the wrist pin bosses only, as the skirt is free from the head on the transverse axis; accordingly, the expansion of the head will tend to stretch, bend or distort the skirt along a diameter parallel to the wrist pin axis, namely, along the diameter B. As a resultof this action, the skirt is contracted or drawn in generally on the transverse diameter A and this contraction tends to compensate for the increase inthe diameter A due to the'thermal expansion of-the skirt itself; accordingly ,diameterA measured between those faces ofthe piston which bear against the cylinder wall is maintained substantially conhas been compensated for by the relief previously described, so that apractically constant seat in,

the cylinder is maintained. Where there is only one of the circumferential slots, such as 0 with the accompanying slots I and bridges III on one side of the piston, then the action is believed to be generally analogous to that described, but restricted in degree due to the absence of one of a the circumferential slots and its accompanying vertical slots and bridges.

In the preceding description, a theory of operation has been suggested; it is to be understood, however, that this theory has been sugseated to facilitate the disclosure and that this invention is not to be limited to any given theory. In practice it has been shown that a piston constructed in the manner shown and described will operate satisfactorily if for a piston of a diameter of 3% inches of an aluminum alloy the piston is fitted with a clearance of 0.002 inch along the diameter A and with a relief of 0.012 inch along the diameter B and with the bridges of the construction as shown and described.

It is further obvious that various changes may be made in the details of construction within the scope of the appended claim without departing from the spirit of this invention; it is, therefore,

to be understood that the invention is not limited m to the specific details shown and or described.

Having thus described the invention, what is claimed is:

A trunk piston of the character described comprising a head, a slnrt havinga greater diameter in the direction of its thrust faces thanin the direction of its wrist pin axis, wrist pin bosses connected to the head, said skirt being continuous at its lower end but provided with slots in the upper region, said slots comprising a circumferential slot adjacent the upper end of the skirt on a face betweenthe wrist pin bosses, and two ion-- gitudinal slots in said face intersecting said circumferential slot and extending downwardly therefrom so as to define a tongue separated on 35 JOHN We. 

